They can prolly be saved. The determining factor will be the amount of rust and pitting that is on the piston and inside the bore. Ive never rebuilt any rear brakes, so the parking brake setup is gonna make it a little more of a pita than a front caliper. That leads me to my next question. Are you sure the parking brake isnt causing the caliper to be stuck? Id say slap it in a vise and work the parking break mechanism. Dont be suprised if this causes the whole piston to pop completely out, which you would want anyways if you are gonna rebuild it. If it doesnt, use compressed air with a blow nozzle, or if that fails, screw a zerk fitting in place of the bleeder and pump in some grease. Use sandpaper or emry cloth to clean up the piston and the bore. The few rear brakes that ive taken apart just to see how they worked, have this screw type deal that pushes on the back of the piston when the lever is moved. Its always nice to be able to take something apart to see how it works and not worry about putting it back together. Be sure to put something in between the piston and the caliper, like a piece of wood, so the piston doest fly outand slam into the other side of the caliper. Oh yeah, lube the new seals with brake fluid also.
